As an optical material including a sealing material for light-emitting diodes (LED), with the change of using environment in recent years, those having not only high optical transparency but also high adhesive properties have been demanded. When the adhesive properties are low, peeling occurs between an LED package and a sealant resin surface. By the occurrence of peeling, reflectivity may decrease, or in the case where the adhesive properties are significantly low, a sealant resin may possibly become unstuck from the package, thus leading to problems on credibility of final products. For example, a surface-packaged type LED is desired to have preferable adhesive properties with package constituent materials such as plastic, ceramics and silver.
On the other hand, as the optical material including a sealing material for light-emitting diodes (LED), with the change of using environment in recent years, those having not only high optical transparency but also high toughness have been also demanded. When the toughness of the sealant resin is low, for example, problems such as generation of a crack in reflowing a solder at the time of packaging an LED occur. Furthermore, problems such as generation of a crack due to irresistible change of using environment e.g. temperature change from high temperatures to low temperatures, etc. may also occur.
In the prior art, a technology applicable to adhesive sheets, finished cloths and the like has been proposed which utilizes a curable composition comprising an organosilicon compound, which is an addition reaction-curable (hydrosilylated) silicone having epoxy group- and alkoxy group-bound silicon atoms, and an organoaluminum compound and showing good adhesive properties (Japanese Kokai Publication Hei-08-183934, Japanese Kokai Publication Hei-05-140459). From the hardness, tucking ability, and optical characteristics viewpoint, however, the materials obtained by this technology are not suited for use as the transparent optical material, particularly the light-emitting diodes. Further, a technology of improving the adhesive properties of addition reaction-curable (hydrosilylated) liquid compositions by adding an epoxy resin and an aluminum compound has been proposed (Japanese Patent No. 3354973). However, there is no disclosure therein about the transparency of the obtained curing product, or the use in optical material, particularly light-emitting diodes.
Further, it has been disclosed that when a condensation reaction-curable silicone is used as a sealing material for building joints, the addition of a borate ester thereto enables manifestation of good adhesion to adherends even when the joints are shallow (Japanese Kokai Publication Sho-59-155483). However, this system is a room temperature curing one, and there is no disclosure either about effect manifestation upon heating for curing or about effect manifestation in the case of application to addition reaction type systems differing therefrom in mode of reaction.
On the other hand, a curable composition is known which comprises an aliphatic organic compound having, within the molecule, at least two carbon-carbon double bonds reactive with a SiH group, a compound containing at least two SiH groups within the molecule, and a hydrosilylation catalyst (WO 01-81475). A curing product obtainable by curing this curable composition can be preferably used as an optical material. However, in applications for films as optical materials, e.g. molded products such as lens, or sealing materials, high mechanical properties are demanded in addition to the optical characteristics in view of long-term reliability of materials. Herein, when the crosslinking density is high, the material becomes fragile, thus a problem of decrease in tensile characteristics arose.
Furthermore, a curable composition containing triallyl isocyanurate as a component has been also proposed (Japanese Kokai Publication Sho-50-100, Japanese Kokai Publication Hei-09-291214). The curable composition described in Japanese Kokai Publication Sho-50-100 is not sufficient in view of heat resistance since the obtained curing product is low in the glass transition temperature. Japanese Kokai Publication Hei-09-291214 does not disclose about the transparency of the obtained curing product from the curable composition, and also there is no disclosure about measures regarding the toughness control of a curing product.